This new project was started as an extension of our previous work that demonstrated a critical role of innate immunity and toll-like receptors (TLR) in pulmonary responses to environmental pollutants. (It has been conducted at Johns Hopkins and will be transferred to NIEHS.) TLRs are known to be important modulators of innate immunity, a critical component of resistance to HIV infection and AIDS progression. TLR4, which mediates responses to Gram-negative bacteria (e.g. lipopolysaccharide or endotoxin) in mouse and humans, has also been implicated as a determinant of HIV infection and viral replication in vitro. We have tested two hypotheses in our study: (1) functional polymorphisms in TLR4 negatively associate with HIV-1 infection; (2) the TLR4 polymorphism confers resistance to disease progression in HIV-infected individuals. In collaboration with the multi-center AIDS cohort study (MACS), we obtained and tested DNA specimens from 501 men: 402 HIV seroconverters (cases) and 99 high-risk HIV negative men (controls). Among seroconverters, 379 had a HIV seroconversion window less <1 yr and AIDS onset window <1 yr (well-defined cases). Individuals were genotyped by single-stranded conformation polymorphism (SSCP) analysis for 896 A to G (Asp299Gly) and 1190 A to G (Thr399Ile) TLR4 polymorphisms that confer resistance to endotoxin. Polymorphisms were confirmed by sequence analysis. To test the first hypothesis (HIV transmission), we compared prevalence of the TLR4 mutations between cases and controls. To test the second hypothesis (AIDS progression), time from seroconversion to AIDS and kinetics of CD4, CD8, and HIV RNA following seroconversion were assessed for the 379 well-defined cases. We found no differences in HIV transmission between HIV negative and positive men for any of the TLR4 genotypes, therefore indicating that the TLR4 polymorphisms were not associated with HIV transmission. However, men heterozygous (+/-) or homozygous (-/-) for the TLR4 polymorphism had significant protection against AIDS onset during the first 8 yr following seroconversion (RR=0.44, 95% CI=0.21-0.89) compared with men homozygous for the wild-type allele (+/+). Interestingly, all men homozygous for either polymorphism (Asp299Gly, n=3; Thr399Ile, n=4) did not develop AIDS (minimum follow up = 10.7 yr). Median HIV RNA following seroconversion was lower in -/- men compared to +/- and +/+ men, but small numbers precluded formal analysis. Our results therefore indicate TLR4 is an important determinant of AIDS progression in HIV-infected individuals, and may provide a potential therapeutic target for treatment of AIDS.